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iEvermore

Could use a hand...

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Hello all, I've been doing pretty well with KSP since I started a few weeks ago. Landed on Duna, Eve, Mun, Minmus, built a handful of stations and ships/landers. My problem is, my main interplanetary ship can make it to Duna, but does not have enough fuel to come back. I get it back into orbit ok but then need to send another ship to dock and and save the Kerbals, thief the leftover fuel and burn back to Kerbin. I'm looking for some Craft files of your interplanetary designs so I can learn from them. If your willing to share your ideas that would be great.

I don't have a picture of my ship since I'm at work. (Working hard or hardly working..)

The current design is

- Docking port

- 1 Roc ASAS

- 1 Roc Mono tank

- 6 landing struts

- a crew module

- a three man pod

- a rover on top that I change up it's release method for none atmospheric planets.

- 6 Small solid boosters to do the first burn to leave Kerbin enroute to Duna. Then they are released

- 12 of the large size cans one on top of the other to make 6 doubles (The cans are same diameter of the Nuke engine's can't remember the name of them)

- 6 Nuke engines

* It makes it into Kerbin orbit full of fuel.

I have it setup to release the upper 6 cans when they are empty and for take off from Duna I can release 4 more to leave 2 fuel cans and the 2 Nuke engines for lift off. This will get it into orbit but not even close enough fuel to head back to Kerbin let alone slow down when I get there.

Also, my additional concerns being that if I can't go and come back from Duna, how am I going to be able to even attempt Jool. I need to learn some better designs.

Thanks in advance for your suggestions.

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No single craft file because it's assembled from 11 launches, but this has made roundtrips while delivering cargoes to Duna, Eve, and Dres.

jkRf7kG.jpg

Here it is carrying the orbiter/lander combo mission payload that I deployed to those worlds.

sUtb3xD.png

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Yes, the nice thing about Duna is that you can aerobrake at both ends of the trip, but the ship in my picture returned from the mission with about 1/3rd of its original fuel remaining, and did make it to Dres and back without aerobraking at the destination.

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I haven't learnt how to Aerobreak just yet. It's on my list of things to learn. This is when you barely enter the atmosphere and allow it to slow you down? I've actually done it once by accident but I find it hard to control. It ended up causing me to force land and I had to reload and try again.

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Yes, aerobraking is very tricky because currently the game gives you no information about how the atmosphere will affect your trajectory. Trial and error through quicksaves is the only way to figure it out. At least in stock. I think some mods do it.

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Ok I will certainly give it a try. Vanamonde very impressive ship. I'll use the pics as a guide.

If anyone can provide a craft file that would still be helpful to dissect it. If not possible then that's ok. I had not thought of putting together a larger ship in orbit. I always found the wobble to be nuts. But I guess I could look into Quantum struts. I try to keep the game as Vanilla as possible.

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I do not have a craft file at hand, but I do have some pointers.

First you should get rid of all unnecessary weight. Like, does the extra crew module have some meaningful purpose? Also, six nuke engines on a moderate size ship is probably overkill. Try something like four or three.

You speaking of getting it back to orbit. Does that mean that you have landed the whole ship to Duna? If so, you should design separate landing and planet transfer stages. That way you don't need to lift so much and you will save fuel.

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I do not have a craft file at hand, but I do have some pointers.

First you should get rid of all unnecessary weight. Like, does the extra crew module have some meaningful purpose? Also, six nuke engines on a moderate size ship is probably overkill. Try something like four or three.

You speaking of getting it back to orbit. Does that mean that you have landed the whole ship to Duna? If so, you should design separate landing and planet transfer stages. That way you don't need to lift so much and you will save fuel.

I originally had 4, I bumped it to 6 because I found I spent too much time at full throttle to land and helped me land with the Rover as well. My Rover is jettisoned by decoupling and using 4 tiny SRB's and then I open 4 chutes to land it about 0.5km away if I time it right. I could do better with a controlled landing with a sky crane like I do on the Mun but I tend to crash it on Duna and find reloading saves a bit of a cheat. It works fine for the Mun since the impact is often light and worst case I rep the wheels. But that's no big deal I guess. I reload plenty of times with failed launches. :P

I mainly put the module on to save the stranded Kerbals but I guess it's not needed. Just evened out the look a little.

I do land the whole ship, but I found that what was left was not much bigger than a lander in the first place. Perhaps removing the module will allow me to remove some of the nuke's. I'm guessing since I'm landing on Duna I could create a small lander that would land with parachutes and limited fuel, which in turn leaves much more for take off. I just need to be able to land the lander, w/Kerbals, and the rover. Perhaps landing all that at once is too heavy... I'll give it a try tonight and then fine tune.

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yeah, aerobraking is either trial and error, or using Mechjeb and its ridiculously accurate predictions. that's all I'm using MJ for these days, it's not even a mod in my mind.

"barely entering the atmosphere" only applies to Jool, and not that much actually - for all the others, you have to push pretty deep to aerocapture into a low orbit.

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yeah, aerobraking is either trial and error, or using Mechjeb and its ridiculously accurate predictions. that's all I'm using MJ for these days, it's not even a mod in my mind.

"barely entering the atmosphere" only applies to Jool, and not that much actually - for all the others, you have to push pretty deep to aerocapture into a low orbit.

No comments about the ship in particular, but one solution I've used is to have 4 engines, 2 x Nuclear and 2 x Aerospikes, with action group activate/deactivate. The spikes are better in atmosphere, more efficient and with 3 x thrust.

Aero braking on Duna, aim for a low of, say, 17,500-18,000 for the first pass, actually 16,500-17,000 is OK and brakes better, but YMMV, test your crafts reaction. Then you need almost no fuel to land on Duna if you target the low lying areas to land in so you have enough time to slow down. I fit 4 x drogue chutes on a stage to trigger early (10-12K), and depending in the mass of the ship, 4-8 normal chutes deployed once you're travelling slow enough. The rogues fully deploy at about 3K up, the standards at 500 m from the ground. You may need engines to decelerate to deploy (or may not) and will probably need them to slow the last 100-150 m to the ground. Use the internal camera © to watch the radar altimeter to get a good feel for the ground height.

I can usually get back and soft land (re packing the chutes is a must !) with either my heavy one piece lander or the light lander plus docking stage. Last time I damaged the docking interplanetary stage and actually made it back fine with just the lander and the fuel left after landing. I'll post pics if I can find them.

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Getting to Duna's surface and back takes 7000-8000 m/s of delta-v, assuming aerobraking at both ends (which you should definitely practice doing, it's massively useful.)

In addition to practicing aerobraking, one of the most important skills you can learn in KSP is how to build minimalist vehicles. It may not matter that you launch a 1000 ton monster to get to the Mun and back, but when you want to do more delta-v intensive missions, figuring out how to get all of the delta-v you can out of your ship becomes a priority, especially once the part count gets high and you can hear your computer's sad little cries for help. If you haven't already, downloading a building mod (like Kerbal Engineer Redux or Mechjeb) can really help with figuring out how to plan out your ship prior to launch.

Once you've got a ship that ought to be able to do the job, it's time to actually get there. That involves good piloting skills, which can really only be improved with practice. Though watching videos (or watching an autopilot fly your ship) can help you figure out how to get around in space cleanly, it takes actually doing it several times to get it right.

Here is a link to a fully functional Duna return vehicle. It has 74 parts and masses something like 65 tons (for the minimalists out there, yes, I fully realize that this can be done in a much much smaller vehicle, but this is reasonable.) I built it with ~8800m/s of delta-v, so there's plenty of wiggle room for messing up.

The staging should work as it is, but if you decide to fire all three chutes at Duna instead of only the first two, you can repack them and deploy using action group 10. The ladder toggles with action group 4.

If you're flying this well, you should be able to get into Low Kerbin Orbit (LKO) using the entire first two stages and about half of the fuel from the third. The remaining fuel in the third stage will get you to Duna and allow about 900 m/s of additional maneuvering if you miss or come in too steeply and need to use the rockets to brake rather than relying primarily on the parachutes. You should go to the fourth stage before landing though, or you'll wind up lithobraking. The fourth stage (just a command module with control stuff, parachutes and legs, an FL-T400 fuel tank, and an LV-909 engine) has enough power and delta-v to get you into Duna orbit and back to Kerbin with ~800 m/s to spare, if used wisely.

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Thanks a lot for the input guys. I'll check our your ship when I get home tonight. I've been practicing the Aero breaking and I'm getting pretty good at it. I've done it twice at Duna already. Still not perfect but I can at least slow down.

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I've been practicing Aero breaking and have figured it out for the most part. But today I had an epiphany and thought I may not be starting the maneuver correctly. I'm starting off by acquiring orbit and then aero breaking to bring down the Apo. But I spend enough fuel burning Retro trying to obtain orbit and bringing the Per to the proper height. (20km on Duna).

What I was thinking today was if I actually need to obtain orbit first or if I can move my Per without getting orbit first.

Here is an Idea of the situation I'm talking about

O = Duna

------ = Trajectory

P = Per

...................O..........................

--------------P------------------

Per is 5,000,000

Now, is there a way I can bring the Per to the correct altitude without having to acquire orbit? How would I go about plotting a maneuver node to do this? Looking at this as a 2 dimensional diagram I would simply need to thrust up to bring my Per closer, but using the Nav ball in 3D to do this is not a simple task. I've only found one video that was in German and he is doing what I want, but I cannot understand how he got his trajectory there in the first place. What I did see though was the Aero breaking took him from escape trajectory to orbit.

I'm figuring this is the most efficient way compared to the way I'm doing it.... Using the blue maneuvers' on the maneuver node does change my "angle of attack" to bring it closer without orbit, but it still seems inefficient. If this is the only way then so be it, but I figured I should ask for input.

Let me know your thoughts.

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Nuke engines aren't so great for landers, especially ones entering the atmosphere. And they are really heavy. I pretty much always make something detachable for the lander. You have to deal with docking in orbit again, but I think that's a lot easier than trying to design such a big lander.

You can definitely bring down the periapsis before getting into orbit. It can be tricky because tiny changes early on in your transit can make big changes to your encounter. But generally I use the 2 blue icons on the maneuver node to get me closer, and I usually do these correction burns at the ascending or descending node so that I can use the purple icons to get the inclination just right. Sometimes you have to fiddle with all 3 axes to get it just right, but this is definitely the best way to set up an encounter.

Edited by DMagic

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I've been practicing Aero breaking and have figured it out for the most part. But today I had an epiphany and thought I may not be starting the maneuver correctly. I'm starting off by acquiring orbit and then aero breaking to bring down the Apo. But I spend enough fuel burning Retro trying to obtain orbit and bringing the Per to the proper height. (20km on Duna).

What I was thinking today was if I actually need to obtain orbit first or if I can move my Per without getting orbit first.

You do not need to achieve capture (orbit) before doing aerobraking. In fact, that's a pretty inefficient way to do it.

Your first approach to the planet should have your apoapsis within the atmosphere. Don't burn retro at this point, just let the atmosphere slow down your ship; this will reduce your speed and, if you do it right, give you your capture (i.e. orbit). You can then leave your apoapsis in the atmosphere if you want to aerobrake a second time to bring your periapsis down further, or else start your burns to get into the orbit you want.

Short version: Use aerobraking for the initial capture.

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So when's the best time to adjust your trajectory to lower the periapsis close enough to aerobrake, assuming no piloting mods?

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The earlier the better! A smaller amount of fuel is needed if you do the maneuver earlier. The later you leave it the more fuel you need correct your trajectory.

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So when's the best time to adjust your trajectory to lower the periapsis close enough to aerobrake, assuming no piloting mods?

As far away as possible. The greater the distance, the less delta-v it will require. I usually go ahead and line up my aerobraking pass with RCS when I make my mid-course plane-change maneuver, weeks or months away from the destination planet.

Setting Conics Mode to 0 in your configuration file so you can zoom in for a better view at the planet helps a lot.

If you want to wait until you're closer (it is easier), do it as soon as you enter the destination SOI. The cost will still be pretty low. Pull the radial handles (up and down ones) on the maneuver planning node to adjust your Pe while in the SOI.

And yeah, definitely do not capture into orbit with your engines then aerobrake... the whole point of aerocapture is that you don't have to burn any fuel to achieve that orbit.

Edited by RoboRay

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As far away as possible. The greater the distance, the less delta-v it will require. I usually go ahead and line up my aerobraking pass with RCS when I make my mid-course plane-change maneuver, weeks or months away from the destination planet.

Setting Conics Mode to 0 in your configuration file so you can zoom in for a better view at the planet helps a lot.

If you want to wait until you're closer (it is easier), do it as soon as you enter the destination SOI. The cost will still be pretty low. Pull the radial handles (up and down ones) on the maneuver planning node to adjust your Pe while in the SOI.

And yeah, definitely do not capture into orbit with your engines then aerobrake... the whole point of aerocapture is that you don't have to burn any fuel to achieve that orbit.

That explains a great many of my early failures with Duna missions...may have to try one of those designs again.

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The earlier the better! A smaller amount of fuel is needed if you do the maneuver earlier. The later you leave it the more fuel you need correct your trajectory.

Very much so. my last Duna mission, I managed to tweak my transfer well enough with two sub-15 m/s correction burns that when I entered Duna's SoI, I had to raise my periapsis to aerobrake, otherwise I'd be lithobraking before the aerobraking had much time to slow me down :-) I set a 9Km periapsis if I remember right, which was enough to go from transfer velocity to a parachute landing in a single maneuver, and that was with Deadly Reentry.

No comments about the ship in particular, but one solution I've used is to have 4 engines, 2 x Nuclear and 2 x Aerospikes, with action group activate/deactivate. The spikes are better in atmosphere, more efficient and with 3 x thrust.

Not quite. Since the ISP is dependent on the atmospheric pressure, and Duna barely has any atmosphere even at "sea level," the atomic engines will still be more efficient. Even at Duna's sea level, I think their ISP is still 680 or so.

That said, most landers I've made with atomic engines that were landing on anything that had close to Duna's gravity wound up getting chemical engines to help out because the low thrust of the atomic engines. Landing on Duna with a local TWR of about 2 is possible, but... unnerving. I think I was at full throttle for the last 8km on my last Duna landing with a TWR that low, and I killed my vertical velocity about 30m above the ground.

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Worked perfectly. Only cost me 450m/s to adjust pernapsis. Much better! I'll work on minimizing it.

Thanks for all your help.

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Or you can just try o take a high pass barely scraping the middle part of the atmosphere and then raise your perafrasis (or however this is called) up a not, so you just scrape the atmosphere and the aerobrake your Apoapsis down to a reasonable level (2-3 are mostly enought). I did this after a EVE transfer at 75000 m hight. Then switched to 80000. Took me 3 passes to get my apoapsis down to ~ 500 km. I did this because my Satalite only had one Ionengine left and was supposed to use this to change the inclanation.

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